1. Field of the Invention
The present invention relates to an ink jet head used for a recording apparatus and a method of fabrication thereof, and in particular to an ink jet head and a method of fabrication thereof in which so-called crosstalks are prevented which otherwise might occur when ejecting ink droplets.
2. Description of the Related Art
An ink jet head used for an ink jet printer is provided with a plurality of drive columns functioning as a drive mechanism, which are constructed by forming a plurality of groves including those crossing the grooves in a piezoelectric element. Diaphragm portions are bonded with adhesive to the column end surfaces of the respective drive columns. Therefore, the drive columns selectively drive the diaphragm portions to eject ink droplets from the selected nozzles.
Such an ink jet head is required to have a high ejection efficiency in order to achieve a high image quality. For meeting this requirement, it is important to bond the diaphragm portions to the end surfaces of the drive columns closely without any gap.
In the prior art, when bonding the end surfaces of the drive columns formed on a piezoelectric element and the diaphragm portions to each other, a gap agent is filled in the gaps formed between the end surfaces and the diaphragms or the amount of the adhesive applied is increased in order to prevent the gaps from forming.
According to Japanese Unexamined Patent Publication No. 8-1932 entitled xe2x80x9cAn ink jet head and a method of fabrication thereofxe2x80x9d, the bonding surface of the piezoelectric element (the end surfaces of the drive columns) are positioned to protrude from the bonding surface of a frame for fixing the piezoelectric element thereby to improve the closeness between the diaphragm portions and the piezoelectric element for an improved ejection efficiency. The technique described in this publication No. 8-1932, in which the diaphragm portions are bonded while being slightly pressed, has produced some effect as far as it improves the closeness.
In the apparatus and the method disclosed in the patent publication No. 8-1932, however, the bonding surfaces of the drive columns (drive end surfaces) to which the diaphragm portions are bonded are flat in shape. The problem is posed, therefore, that the adhesive leaks out and attaches to adjacent drive columns at the time of bonding and crosstalks are liable to be caused when ejecting ink droplets. This problem has become more serious as the pitch of the drive columns of the piezoelectric elements has been increasingly shortened with the increase in the degree of integration.
An object of the present invention is to provide an ink jet head, which can achieve reliable ejection of ink droplets.
Another object of the present invention is to provide an ink jet head having a structure in which the adhesive that has leaked out at the time of bonding is prevented from attaching to adjacent drive columns and method of fabrication of such an ink jet head.
According to an aspect of the present invention, an ink jet head includes a plurality of drive columns arranged in parallel, each of the drive columns comprising a piezoelectric member; and a plate having a plurality of diaphragm portions which are bonded to end surfaces of the drive columns with an adhesive, respectively. Each of the diaphragm portions is driven by a drive column corresponding to the diaphragm portion thereby to eject ink droplets. At least one of each of the diaphragm portions and the drive column corresponding the diaphragm portion comprises an accommodating groove for accommodating an excess adhesive produced when bonding the diaphragm portion to the end surface of the drive column.
Each of the drive columns may comprise the accommodating groove. The accommodating groove is preferably a rack portion formed one step lower than the end surface of the drive column along a peripheral edge of an end portion of the drive column. The rack portion may be formed along the entire peripheral edge of the end portion. The accommodating groove may be a recess formed in the end surface of the drive column. Alternatively, each of the diaphragm portions may include the accommodating groove. The accommodating groove may be a recess formed in the diaphragm portion.
According to another aspect of the present invention, a method of fabricating an ink jet head, includes the steps of: a) forming a plurality of grooves including those crossing said grooves in a piezoelectric element to form a plurality of drive columns; b) forming an accommodating groove in each of the drive columns, wherein the accommodating groove is designed to accommodate an excess adhesive which is produced when bonding the diaphragm portion to the end surface of the drive column; and c) bonding the diaphragm portion to the end surface of the drive column with an adhesive.
In the step a), a cutting tool of a predetermined width may be used to form the grooves to produce the drive columns each shaped like a rectangular solid. In the step b), the cutting tool may be also used to form a rack portion one step lower than the end surface of the drive column along a peripheral edge of an end portion of the drive column to produce the accommodating groove. In this case, the rack portion may be formed by using the cutting tool shifted from a position set in the step a) by a predetermined distance.
Alternately, in the step a), a first cutting tool having a first width may be used to form the grooves to produce the drive columns each shaped like a rectangular solid. In the step b), a second cutting tool having a second width wider than the first width may be used to form opposite rack portions of adjacent drive columns to produce the accommodating groove, wherein a rack portion is formed one step lower than the end surface of the drive column along a peripheral edge of an end portion of the drive column.
As described above, the accommodating groove is formed in the drive column or the diaphragm portion to accommodate an excess adhesive which leaks out at the time of bonding the diaphragm portion and the drive column to each other. Therefore, even in the case where the pitch of the drive columns has been increasingly shortened with the increase in the degree of integration, the excess adhesive is prevented from attaching to the adjacent drive columns and thus causing crosstalks at the time of ink droplet ejection to be effectively suppressed.